Gas mixing device



Dec. 23, 1958 R. c. oNAN ET AL 2,865,389

' GAS MIXING DEVICE 2 SheeLs--Sheerl 1 Filed May 2, 195@ INVENTORS P06527' C. ONAA/ BY C/HELES 5. Ha/E AT1-a Nfy' Dec. 23, 1958 Filed May 2, 1956 O E/g. L

R. C. ONAN ET AL GAS MIXING DEVICE 2 Sheets-Sheet 2 i myV/Ill l IN V EN TOR Poseer c. o/mw (2f/A2455 J. Hox E A 7' 70E/VE Y United States Patent `GAS MrxrNG DEVICE Robert C. Onan and Charles S. Holte, Milwaukee, Wis.,

assignors to Waukee Engineering Company, Inc., Milwaukee, Wis., a corporation of Wisconsin Application May 2, 1956, Serial No. 582,213

9 Claims. (Cl. 137-111) This invention relates to improvements in carburetting or mixing devices for gases whereby a plurality of gases may be combined in predetermined proportions and in quantity depending on relative gas pressures, for combustion or other chemical reactions.

lt is therefore an object of the present invention to provide a device for mixing gases in given proportions and in which the proportioning means is accurately and easily adjustable to conditions known prior to or occurring during use of such device.

Another object of the invention is to provide a device for proportionally mixing gases and in which the areas of standard size ports in a casing are initially adjustable to a range of average conditions to be met, by a member interchangeably secured in the casing and are adjustable during operation of the device to exactly the conditions to be met by simple change in shape of the interchangeable member.

Another object of the invention is to provide a device for the proportional mixing of gases, in which one standard casing forms the major and most costly part of the device and only the interchange of a minor part is required to adapt the device to the conditions required for combination of any two gases, and in which movable parts are easily and quickly removed and replaced after cleaning or change of parts.

Another object of the invention is to provide a device for the proportional mixing of gases and in which the proportioning of the gasesmay be varied automatically as the ratio of a condition of one gas to a condition of the gas mixture changes responsive to reaction conditions.

Another object of the invention is to provide a device for the proportional mixing of gases, which can be readily mounted on a panel adjacent measuring registers and recorders without impairing ease of change of parts to meet changes in reaction condition, ease of inspection and removal of parts for cleaning for insuring accurate operation of the device and maintenance of the device in its best operating condition.

Another object of the invention is to provide a device for the proportional mixing of gases, which is fully sealed and can be used with various combinations of any two gases, without leakage of gases from the device or change in proportions of the gases or contamination of the gases by leakage of air into the device.

Another object of the invention is to provide a device for the proportional mixing of gases, in which neither the means for controlling the proportions of the gases admitted to a mixing chamber nor the means for controlling the volumes thereof, react on and interfere with `the operation of the other means.

Another object of the invention is to provide a device for proportional mixing of gases, with indicating means whereby the gas proportioning means may be returned exactly to its original position after changes in the position therefor during use of the device.

A further object of the invention is to provide a device for the proportional mixing of gases which is provided Patented Dee. 23, 1958 ice with a reverse flow check valve operative free from linkpressure drop during operation of the device.

Advantages and objects other than those above set forth will be apparent from the following description when read in connection with the accompanying drawings in which:

Fig. 1 is a perspective view of an assembled device embodying the present invention;

Fig. 2 is a crosssection taken on the vertical plane of line 2-2 in Fig. l;

Fig. 3 is an elevation of the rear side of the device;

Fig. 4 is a cross-section taken on-the horizontal plane of line 4--4 in Fig. 2;

Fig. 5 is a cross-sectional view taken on the vertical planes of broken line 5--5 in Fig. 4; t

Fig. 6 is a cross-sectional view on the vertical plane of line 6 6 in Fig. 4;

Fig. 7 is an enlarged plan view of a closure and indicating scales associated with the mixing chamber of the device;

Fig. 8 is a perspective view of two port members of the gas proportioning means employed;

Fig. 9 is a fragmentary end View of the proportioning members in one position relative to the ports between the inlet chambers and the mixing chamber;

Fig. l0 is a view similar to Fig. 9 but showing the proportioning members in different positions; and

Fig. ll is a diagram of the relative positions of the proportioning members and of the volume control valve when a port area is to be varied dependent upon the position of the valve.

Generally, the present gas carburetting or proportional gas mixing device comprises a casing providing a lirst inlet chamber and a second inlet chamber to which gases are separately supplied, and a third or mixing chamber with an outlet and which is accessible from both ends of the chamber. Partitions in the casing itself are formed with ports connecting the inlet chambers with the mixing chamber and such ports have ixed and equal areas of at least the size which may be required for volumes of gases in any combination now in use. The port areas are initially proportioned to a predetermined relationship of the gases by a first proportioning member in the form of a segment of a tube secured to the inside of the mixing chamber and extending in part over both ports. The segment is easily and quickly replaceable by other segments limiting the port openings to different total areas or to different proportions dependent on the volumes of gases iiowing therethrough. A second proportioning member in the form ot a movable tube coeacts with the xed segment for finer adjustment of the effective port areas to a predetermined proportioning of the gases when the gas reaction varies within a usual range of conditions. Co-acting edges of the segment and tube are readily shaped to give an automatic change in gas proportions as the volume of flow changes due to change in the reaction or total demand. The movable proportioning member is adjustable by a micrometer-type screw device for eliminating back-lash and extending from one of the inlet member chambers through a seal in the casing wall for ready removal and replacement as a unit. The mixing chamber has a closure, for one of its open ends, with a transparent window for observation of moving parts of the device and'a reference scale is fixed adjacent the closure window for co-action with a reference mark on or attached to the movable proportioning member.

A` piston-like valve controls the size of the port openings in use at any particular time, as it reciprocates inside the port area proportioning segment and tube to vary the volume of gases admitted to the mixing chamber responsive to demand and upon ilexure of a diaphragm at the other end of such chamber. The diaphragm is under t the pressure of the gas in one inlet chamber and of the mixture of the gases in the mixing chamber. The rod connecting the valve with the diaphragm is rectangular and is heldfragainst turning by a guide in the mix" i" chamber to reliev'efthe diaphragm of anytorsional forces acting" on the valve during placement inorremoval, from thecasing.V Anoutlet check valveis provided for the mixing chamber and isa simple disk' tilting on a portion of its edge between Va seat and a stop in the outlet.` The checli'valve is biased to seated position only by a counter Weight to maintain sensitivity oi the valve minimize gas pressure drop due to the valve.

Referringspecically to the drawing by reference nurnerals,` l5 generally designates an approximately rec# tangular casing .providing a first gas yreceiving chamber i6 and a second-gas receiving chamber El? with respect-.rc inlet openings lb and i9, and a gas mixing chamber 2f?. witlran outlet23. The mixingror third chamber is preferably cylindrical `with its axis at a: right angle from one or-more' casing surfaces and is open-at'both ends for the entrance of tools for shaping the mixing' chamber. Thel gas- Vreceiving chambers and the mixing chambers are respectively connected by ports Zland 2:5 which are preferably oi equal areas so that either one oli 'the inlet chambers may be used for any one of a number kof gases and which will be of adequate size for a large number of gases in various combinations. The casing is 'preferably a casting-for low cost and gas-tight construction and the whole ot the mixing chamber walls are accessible from outside the castingfor shaping, the ports being merely rough openings in internal casing walls.

One end of the mixing chamber 22 has a closure comprising a ring 3d with a window 3l, the ring being threaded to engage with the casing. A reference line 32 is placed on the casing window and a reference scale 33 co-acting with the line 32, is detachably secured to a moving member, the'scaie being preferably closely adjacent to the casing window. The other end or" the mixing chamber is closed by a removable plate 36 which co-acts with the casing to retain a liexible diaphragm 37 to which is attacheda rod 3S as by the use of slates The rod 32E ispreferably a shape other than circular and extends through a. similarly shaped hole in a guide itl te avoid torsionl on the diaphragmupon assembly or disassembly of other parts of the device. is held in thel mixing chamber by a retaining ring il which may also serve as positioning or bearing means for other parts.

Because the areas of the casing ports 24 and d made equal 'for simplicity in casting the casing and arc large to allow use of one casting for any gas combina tions Vin the volume likely to be required, means are provided for interchangeably securing an initial proportioning of the port areas. One member of such means coinprises a segment ot' a tube .16 of which the outer surance seats on` the wall of the mixing chamber 22 and which has any desired :internal diameter' but preferably that of the guide-retaining ring 4i. in the present embodiment the segment S6 is shown as being positioned by the guidering il and therefore as requiring only one screw to hold the segment removably in place. However, the ring il need notserve also to position the segment as the segment can be positioned on a seat machined in the casing or canbeheld by only two screws accessible from exn ternally of thecasing for ready interchange of the seg-- ment.- The segmentV is shown as extending only a small distance over one port and a considerable distance over the other port, but such distances depend on the initial proportioning desired between the port opening areas.

Another member of theport area proportioning means is a tube 47 having a wall extension i8 of a size peripherally of the extension, which is substantially the dif ference between the inner periphery oi the mixing charnber and the VperipheralV length of the segment ed. The outer diameter of the tube 47 is such that the tube has The guide fill is part of or 4. an easy rotatable t in the mixing chamber and the inner diameter of the tube is preferably that of the ring 41 and the segment 46. The tube 47 may rest at one edge on the retaining ring il and by another edge on the segment 46 or may rest on a seat machined in the casing. The movable parts are preferably of so-called self-lubricating metal for continued easy operation.-

The tube 47 has an external groove 49 extending from one edge thereof to receive a part of a unit sub-assembly 'for rotating the tube. Such unit comprises asupport'Sl.

ending from outside the casing intoone of the'inlet chambers and herein shown asbeinga part of a plugSS iitting into an opening in the chamber wall and having a flange 56 by which the plug is attached to the casing. An aperture in the plug 55 is provided with a seal 57 through which the stem of a screw 58 extends and which bears in the plug, and the screw stem carries a handwheel E9. A nut 62 engages the screw 58 and-travels in the support 54 axially ofthe screw and the support, the support holding the screw againstrotation. The nut has mounted therein a pin 63'having a spherical head engageable in the groove 49 in tube 4'7" andthe pin is movable along its own axis under the resistance of a spring d4. line adjustment of the proportioning means.

A ilexible connection is thus made between the screw 53 and the tube 47 whereby the tube is rotatable in the mixing chamber upon :the turning of the screw to secure movement of nut 62 and pin 63`axially of the screw, the spring 64 permitting movement of the pin 632- along its own axis. The Wall extension 4S of the tube is thus movable to bring two of its edges into any desired spatial relation with the respectively corresponding edges of the segment das shown in Fig. 9 where the port 255 is approximately one-third the effective area ot the port or where the port Z4 is opened wider and the port 25 is substantially closed. One of the ports may of course be fully closed if desired. The various joints at the closure 3d, 3l and parts Sil 56 are sealed by suitable gaskets and plate 36 is sealed by the diaphragm acting as a gasket.

it will be noted that the tube 47 also extends below the.

upper edges of the ports 2f and 25 so thatthe effective areas of such ports are deined by an edge of the ring 41, an edge of the segment 46 and two edges of the tube 47.

provide a seat or seats in the casing for positioningthe segment and to serveas thel bearing for the-wall exten-v sion of the tube.

The co-acting end edges'67 yand 680i segment d'and' tube 47' are usually formed forbearing of the tube on the segment. However, the co-acting side edges 69 and 7d of the segment or the tube, or both, may be formed Thus, ythe effective-port area or both areas, may be.

differently shaped depending on the characteristics of the gas handled and the manner in which such characteristics affect the processing at -dilerent times. For example, in endothermic reactions the proportions of thegases may require varying ,during the reaction, i. e., a leanergasfY air' mixture may be used when the reaction yrequires a low quantity of the mixture, than. when a greater quantity is .required to provide a given water vaporcontent'in thereaction product. O'r` when the .process involves a The screw and nut are of micrometer type forV .lf the ring 41 does not also serve as positioning` and bearing means for the segment 41 and tube 47,- and, an edge ofsuch ring does not also serve to deiine 'one` edge of the-eiiective area'ot thepo-rts, it is necessary to catalyst of given area, the ratio of the gas mixture flow to catalyst area may require that the` ratio ot-the gas mixture be reduced as the velocity of mixture flow in- Or, under some conditions, the reaction may be carried out at two or more different points or at a succession of points. A change in both areas may then Ibe desired even though the pressure of the gas mixture may not be changed. The segment edges 69 and the tube edges 7b are easily formed to give any desired shape or area to either or both ports. i

ri`he degree of opening of the proportioning ports, is controlled by a valve 75 having a piston-like shape with a cylindrical surface of approximately the Width of the dimension ot ports Z4, 25' in the Vdirection of movement of the valve. rThe piston-like end surface ofthe valve has an aperture 7o for equalizing the pressure of the mixed gases on the two sides ofthe valve. Astem 77 is rotatably attached axially of the valve with one end exposed on one side of the valve and provided with a threaded socket to receive the threaded end of the diaphragm rod 38. The stern 77 is however secured to the valve and cannot-drop .accidentally into the device. The other end of the valve stem 77 is slotted to receive a tool for screwing the valve stern to the diaphragm rod. The valve 7d has a free sliding fit in the tube 47 and is reciprocated in such tube as the diaphragm 37 flexes. One side of the diaphragm is subjected to the pressure in one inlet chamber by Way of a passage 7S while the other side ol? the diaphragm is subjected to4 the pressure of the gas mixture.

Une inlet chamber will usually be supplied With air or other gas at atmospheric pressure and the `diaphragm is therefore responsive to variations in reaction which vary the demand for and pressure of the gas mixture. As the demand for the gas mixture increases, the pressure in the mixing chamber decreases so that the diaphragm llexes upwardly and lifts the control valve.` The control valve opens both ports farther by the same amount unless the edges of the segment i6 or the tube i7 are at an angle to each other or are shaped otherwise than as parallel edges which are parallel to the axis of the control valve. Such angularity or other shaping of either the edge 69 or lli or both such edges varies the proportions of the gases responsive to the demand without change in the gas proportions at the beginning of or at other given points of the reaction. j

'lfhe outlet 23 from` the mixing chamber 22 has a valve seat S2 formed about its periphery anda pipe nipple d3 is attached to the casing 15 and is, in fact, an extension of the outlet. The nipple provides two abutments tid, 85 of which the end of abutment 84 coacts with the casing in detining a notch-like space. A disk S6 rests on its edge in the notch and may tilt away from its seat d2. until such tilting is stopped by the abutment 85. The valve has a threaded arm extending therefrom to ward the mixing chamber 22 to support a number of counter-weights 7 which bias orurge the valve toward its seat against the pressure of the gas mixture flow past the valve. T he Weights are adjustable to allow counter weighting for opening of the valve only when ilow of gas mixture takes place so that even a small back pressure in the nipple will co-act with the weights in closing the valve.

lt will therefore be seen that the present invention provides a casing and other parts which can be made in one standard size for many combinations (volumes) of gases and for varying conditions during use of such combinations, with the work for internal nishing of the casing coni-ined to only one chamber open at both ends and with such work reduced to a minimum. A tube segment and a tube are individually shaped at only their co-acting edges to adapt the Idevice exactly to any combination of gas and any conditions occurring in such combinations at different times during a reaction. An initial or gross proportioning is obtained by the :proper sizing and placing of the segment and the segment is readily interchanged with other segments depending on p the gas combination or reaction conditions. Neither the gas proportioning means nor the gas volume controlling means affect the operation of the other and tine adjustment can be made otthe proportioning means. Such adjustment can `be changed to a degree shown on a scale and can be returned exactly to its prior setting, The closure window allows observation of the relatively moving parts land determination of when cleaning is required or that the parts are operating satisfactorily at variouslow conditions. The closure is a simple ring removable and replaceable Without tools. The adjustment for the gas proportioning means is a micrometer 'screw unit which is fre-e from back-lash and is easily and quickly removed and replaced by a clean unit to preserve accuracy and ease of adjustment. A simple tilting disk and its biasing weights provide a check valve free from parts requiring frequent cleaning and which increase resistance to gas flow even when clean. The entire device is sealed against leakages and can therefore be used for any combinations of any gases.

Various changes and modicatinns may be made in the embodiment of the invention herein disclosed, without departing from the spirit of the invention or from the scope of the appended claims.

We claim:

l. In a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers each having an'inlet and a gas mixing chamber having an outlet and having ports therein connecting each receiving chamber with the mixing chamber, a segment oi a cylindrical tube interchangeably mounted in the mixing chamber for partially dening the open area of the several ports, a cylindrical tube rotatable in the mixing chamber and having a Wall portion co-acting` with the segment for partially defining the open area of the ports, means extending into one receiving chamber through the casing wall and in sealed relation therewith for rotating the tube to Vary the open area of the ports, said means being removable and replaceable as `a unit Without affecting other movable portions of the device, a valve reciprocable in the tube segment and tube for controlling the `volume of gas owing from the receiving chambers into the mixing chamber, means responsive to the gase pressure in one receiving chamber, and in the mixing chamber for reciprocating the valve, a rod connecting the pressure responsive means with the valve, and means for guiding movement ot' he rod to pre vent torsion of the pressure responsive means and coacting with the segment and the tube in defining the` open area ofthe ports.

2. In a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers eacbhaving an inlet and a gas mixing chamber having an outlet, the ctfog having ports therein connecting each receiving ch Ynber with the mixing chamber, a segment of a cylindrical tube interchangeably mounted in the mixing chamber for partially defining the open area of the several ports, a cylindrical tube vrotatable in the mixing chamber and having a wall portion coacting with the segment for partially dening the open area of the ports, means extending into one receiving chamber through the casing Wall and in sealed relation therewith for rotating the tube to vary the open area of the ports, a valve reciprocable in the tube segment and tube for controlling the volume of gas owing from the receiving chambers into the mixing chamber, means responsive to the gas pressure in one receiving charnber and in the mixing chamber for reciprocating the valve, a rod connecting the pressure responsive means with the valve, and means for guiding movement of the rod to prevent torsion of the pressure responsive means and co-acting with the segment and the tube in defining the ,open area of the ports, pairs of edges of the segment and the tube being shaped to deiine non-rectangular open areas of the ports.

3. ln a gas mixing and proportioning device, a .unitary casing providing a plurality of gas receiving chambers each having an inlet and a gas mixing chamber ha'ing an outlet, the casing have ports therein connecting each receiving chamber with the mixing chamber, a segment of a cylindrical tube interchangeably mounted in the mixing chamber for partially deiining the open area of the several ports, a cylindrical tube rotatable in the mixing chamber andhaving a wall porti n coacting with the segment for partially defining the open area of the ports, means extending into one receiving chamber through the casing wall for rotating the to vary the open area of the ports, said means move le and replaceable as a unit without ting other movable portions of the device and comprising a plug sealed in the receiving chamber opening having a projection therefrom, a nut slidably supported by the plug projection, a screw extending through the plug and sealed therein for engagement with the nut, and resilient means movably mounted in the nut and engageable with the tube.

4. in a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers each having an inlet and a gas mixing chamber having an outlet, the casing having ports therein connecting each receiving chamber with the mixing chamber, a segment of avcylindrical tube interchangeably mounted in the mixing chamber for partially defining the open area of the several ports, a cylindrical tube rotatable in the mixing chamber and having a wall portion 2o-acting with the segment for partially defining the open area of the ports, means extending into one receiving chamber through the casing wall for rotating the tube to vary the open area of the ports, said means being removable and replaceable as a unit without affecting other Inovable portions of the device and a plug sealed in the receiving chamber opening and having a hollow cylindrical projection into the chamber, the projection being slotted from one end, a nut slidably supported in the plug projection, a screw extending through the plug and sealed therein for engaging the nut, anda pin movably mounted in the nut and resiliently urged into engagement with the tube for rotation thereof, the pin being guided in the slots at the end of the plug projection. y

5. in a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers cach having an inlet and a gas mixing chamber having an outlet and having ports therein connecting each receiving chamber with the mixing chamber, a segment of a cylindrical tube interchangeably mounted in the mixing chamber for partially deining the open area or the several ports, a cylindrical tube rotatable in the mixing chamber and having a wall portion co-acting with the segment for partially defining the open area of the ports, means extending into one receiving chamber through the casing wall and in sealed relation therewith for rorating the tube to vary the open area of the ports, a valve reciprocable in the tube segment and tube for controlling the volume of gas flowing from the receiving chambers into the mixing chamber, stem rotatably secured to the valve and extending on both sides thereof, means responsive to gas pressure in one receiving chamber and in the mixing chamber for reciprocating the valve, and a rod connectible with the valve stem upon rotation of the stem, and means for guiding movement of the rod to prevent torsion of the diaphragm upon connection of the stem with the rod, an edge of the segment aiding in defining the open area of one port and being at an langle to the center line of the mixing chamber forli/Varying the ratio or". port openings as the rate of ilow of gases varies.

6. ln a gasrnixing and prop ortioning device, `a unitary casing providing a plurality of gas receiving chambers each havingan inlet and a gas mixing chamber having I casing, a segment of a cylindrical tube interchangeablymounted in the mixing chamber for partially dening the open area of theseveral ports, a cylindrical tube rotatable in the mixing chamber and having a wall portion co-acting with the segment for partially defining the open area of the ports, means extending into one re ceiving chamber through the casing wall and in sealed relation therewith for rotating the tube to vary the open area ofthe ports, a valve reciprocable in the tube segment andtube forrcontrolling the volume of gas owing 'from thereceivirig chambers into the mixing chamber, means responsive to the gas pressure in one receiving chamber and in the mixing chamber for reciprocating the valve, a rod connecting the pressure responsive means with the valve, meansfor guiding movement of the rod to prevent torsion of the pressure responsive means and coacting with the segment and the tube in dening the open area of the ports, a readily removable closure at one end of the mixing chamber providing a window for observation of relatively movable parts within the casing, and a referance scale attached to the tube and visible through the window, the window having a zero line for coaction with the scale.

7. `In a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers each having an inlet and a gas mixing chamber having an outlet andhaving ports thereinconnecting each receiving chamber with the mixing chamber, the mixing chamber being open at both ends to exteriorly of the casing, a segment of a cylindrical tube interchangeably f mounted in the mixing chamber for partially deiining the open area of the several ports, a cylindrical tube rotatable in the mixing chamber and having a wall portion coacting with the segment for partially dening the open area of the ports, means extending into one receiving chamberthrough the casing wall and in sealed relation therewith for rotating the tube to vary the open area `of the ports, a valve reciprocable in the tube segment and tube for controlling the volume of gas owing from the receiving chambers into the mixing chamber, means responsive to the gas pressure in one receiving chamber and in the mixing chamber for reciprocating the valve, a rod connecting the pressure responsive means with the valve, means for guiding movement of the rod to prevent torsion of the pressure responsive means and co-acting with the segment and the tube in defining the open area of the ports, a transparent plate closing one end of the mixing chamber and having a zero line thereon, a ring engaging the casing for holding the plate in sealed relation thereto,

and a reference scale attached to the end of the tube and visible through the plate for co-action with the zero line in indicating the position of the tube relative to the segment.

8. In a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers each having an inlet and a gas mixing chamber having an outlet and having ports therein connecting each receiving chamber with the mixing chamber, the mixing chamber being open at both ends to exteriorly of the casing, a segment of a cylindrical tube interchangeably mounted in the mixing chamber for partially dening the open area of the several ports, a cylindrical tube rotatable in the mixing chamber and having a wall portion co-acting with thesegment for partially delningthe open area of the ports, means extending into one receiving chamber through the 4casing wall and in sealed relation therewith for rotatingthe tube to vary the open area `of the ports, a valve reciprocable in the tube segment and tube for controlling the volume of gas flowing from the receiving chambers into the mixing chamber, means responsive to thegas pressure in one` receiving chamber and in the mixing chamber for reciprocating the valve, a rod connecting the pressure responsive means with the valve, means for guiding movement of the rod to prevent torsion of the pressure responsive means and co-acting with the segment and the tube in defining the open area of the ports, an outlet nipple attached to the casing at the mixing chamber outlet, a valve movable to open position limited by the outlet nipple, and adjustable weights associated with the valve and urging the valve toward closed position.

9. In a gas mixing and proportioning device, a unitary casing providing a plurality of gas receiving chambers each having an inlet and a gas mixing chamber having an outlet and having ports therein connecting each receiving chamber With the mixing chamber, the mixing chamber being open at both ends to exteriorly of the casing, a segment of a cylindrical tube interchangeably mounted in the mixing chamber for partially defining the open area of the several ports, a cylindrical tube rotatable inthe mixing chamber and having a wall portion co-acting with the segment for partially defining the open area of the ports, means extending into one receiving chamber through the casing wall and in Isealed relation therewith for rotating the tube to vary the open area of the ports, a valve reciprocable in the tube segment and tube for controlling the volume of gas flowing from the receiving chambers into the mixing chamber, means responsive to the gas pressure in one receiving chamber and in the mixing chamber .for reciprocating the valve, a rod connecting the pressure responsive means with the valve, means for guiding movement ofthe rod to prevent torsion of the pressure responsive means and co-acting with the segment and the tube in defining the open area of the ports, an outlet nipple attached to the casing at the mixing chamber outlet, a valve positioned by the casing -and the stationary nipple, abutments in the nipple limiting movement `of the valve in one direction, and Weights overhung from the valve toward the mixing chamber for urging the valve towa-rd closed position.

References Cited in the le of this patent UNITED STATES PATENTS 1,980,770 Thomas Nov. 13, 1934 2,252,152 Work Aug. 12, 1941 2,486,017 Furkcrt Oct. 25, 1949 

